I have two lists of 2 different types of classes. I want to select all of the items in the first list that have a property (we'll call it name) that do not have coresponding objects with same name in another list.
For example if I have a list of Age items (joe, 4), (marry,5), (ed,2)
and another list of relation items (joe,father), (ed,brother)
I want to end up with a resulting list of (marry,5)
I was not sure if "except" was somehow used here.
Given two arrays (I'm using anonymous types here, but it's the same deal with proper classes) of different types, you're going to need to extract the excepted 'key' first. In this case the 'key' is the Name property.
//Setup
var ageItems = new [] { new {Name = "Joe", Age=4}, new {Name = "Marry", Age=5}, new {Name="Ed", Age=2} };
var relationItems = new [] { new {Name="Joe", Rel = "Father"}, new {Name="Ed", Rel="Brother"} };
//Get the names
var exceptedNames = ageItems.Select (a => a.Name).Except(relationItems.Select (r => r.Name));
//At this point, we have an `IEnumerable` containing 'Marry', we need to get the instances
var exceptedItems = ageItems.Where(a => exceptedNames.Contains(a.Name));
Of course, being LINQ, you can whack it all into one call:
var exceptedItems = ageItems.Where (a => ageItems.Select (b => b.Name).Except(relationItems.Select (r => r.Name)).Contains(a.Name));
You can't use the .Except overload that takes an IEqualityComparer instance as your classes differ, and IEqualityComparer can only compare two items of the same type, hence we have to generalise and pull out the same fields.
Related
I am trying to create table headers that sort during a back end call in nhibernate. When clicking the header it sends a string indicating what to sort by (ie "Name", "NameDesc") and sending it to the db call.
The db can get quite large so I also have back end filters and pagination built into reduce the size of the retrieved data and therefore the orderby needs to happen before or at the same time as the filters and skip and take to avoid ordering the smaller data. Here is an example of the QueryOver call:
IList<Event> s =
session.QueryOver<Event>(() => #eventAlias)
.Fetch(#event => #event.FiscalYear).Eager
.JoinQueryOver(() => #eventAlias.FiscalYear, () => fyAlias, JoinType.InnerJoin, Restrictions.On(() => fyAlias.Id).IsIn(_years))
.Where(() => !#eventAlias.IsDeleted);
.OrderBy(() => fyAlias.RefCode).Asc
.ThenBy(() => #eventAlias.Name).Asc
.Skip(numberOfRecordsToSkip)
.Take(numberOfRecordsInPage)
.List();
How can I accomplish this?
One way how to achieve this (one of many, because you can also use some fully-typed filter object etc or some query builder) could be like this draft:
Part one and two:
// I. a reference to our query
var query = session.QueryOver<Event>(() => #eventAlias);
// II. join, filter... whatever needed
query
.Fetch(#event => #event.FiscalYear).Eager
var joinQuery = query
.JoinQueryOver(...)
.Where(() => !#eventAlias.IsDeleted)
...
Part three:
// III. Order BY
// Assume we have a list of strings (passed from a UI client)
// here represented by these two values
var sortBy = new List<string> {"Name", "CodeDesc"};
// first, have a reference for the OrderBuilder
IQueryOverOrderBuilder<Event, Event> order = null;
// iterate the list
foreach (var sortProperty in sortBy)
{
// use Desc or Asc?
var useDesc = sortProperty.EndsWith("Desc");
// Clean the property name
var name = useDesc
? sortProperty.Remove(sortProperty.Length - 4, 4)
: sortProperty;
// Build the ORDER
order = order == null
? query.OrderBy(Projections.Property(name))
: query.ThenBy(Projections.Property(name))
;
// use DESC or ASC
query = useDesc ? order.Desc : order.Asc;
}
Finally the results:
// IV. back to query... call the DB and get the result
IList<Event> s = query
.List<Event>();
This draft is ready to do sorting on top of the root query. You can also extend that to be able to add some order statements to joinQuery (e.g. if the string is "FiscalYear.MonthDesc"). The logic would be similar, but built around the joinQuery (see at the part one)
I have an Action method in my controller which returns a List Object
Public ActionResult GetCats(long Id,string strsortorder,string dltIds)
{
var Result=objrepo.GetCats(Id);//this method returns me List of Result
}
My array looks like this:
var Result=[{CatId:1015,CatName:Abc},{CatId:1016,CatName:Acd},
{CatId:1017,CatName:Adf},{CatId:1018,CatName:CDdf},{CatId:1019,CatName:asdas},
{CatId:1020,CatName:Abc},{CatId:1021,CatName:Abc},{CatId:1022,CatName:Abc},
{CatId:1023,CatName:Abc},{CatId:1024,CatName:Abc}]
What I want to do is:
Using two more parameters in my Action Method "strsortorder" and "dltIds"
that have a list of ids like this:
strsortorder="1021,1015,1016,1019,1022";
dltIds="1017,1018,1020";
From this the "Result" returned from my method , I want to remove the records which are in "dltids" and the remaining array should be sorted in the order which I have in "strsortorder";
In the end the new object should look like this:
var NewResult=[{CatId:1021,CatName:Abc},{CatId:1015,CatName:Abc},
{CatId:1016,CatName:Acd},{CatId:1019,CatName:asdas},{CatId:1022,CatName:Abc},
{CatId:1023,CatName:Abc},{CatId:1024,CatName:Abc}]
Can any one help me in acheiving this in linq or any other way?
I want to avoid any type of loop or froeach here for max extent, I know it can be done by looping but I want to avoid this since the result can sometimes contain large amounts of data.
I realized you can use an ArrayList instead of a Dictionary and it would be faster. I think Dictionary is clear how it works but here is the "better" implementation using array list:
var excludeList = dltIds.Split(",".ToCharArray());
ArrayList sortList = new ArrayList(strsortorder.Split(",".ToCharArray()));
var NewResult =
Result.Where(item => ! excludeList.Contains(item.CatId.ToString()))
.OrderBy(item => {
if (sortList.Contains(item.CatId.ToString()))
return sortList.IndexOf(item.CatId.ToString());
return sortList.Count;
});
Original answer below:
Public ActionResult GetCats(long Id,string strsortorder,string dltIds)
{
var Result=objrepo.GetCats(Id);//this method returns me List of Result
var excludeList = dltIds.Split(",".ToCharArray());
int orderCount = 0; // used in the closure creating the Dictionary below
var sortList = strsortorder.Split(",".ToCharArray())
.ToDictionary(x => x,x => orderCount++);
// filter
var NewResult =
Result.Where(item => ! excludeList.Contains(item.CatId.ToString()))
.OrderBy(item => {
if (sortList.ContainsKey(item.CatId.ToString()))
return sortList[item.CatId.ToString()];
return sortList.Count();
});
}
How this works:
First I create lists out of your comma separated exclude list using split.
This I create a dictionary with the key being the ordering ID and the value being an integer that goes up by one.
For the filtering I look to see if an item is in the exclude array before I continue processing the item.
I then do a sort on matching against the key and the dictionary and returning the value -- this will sort things in the order of the list since I incremented a counter when creating the values. If an item is not in the dictionary I return one more than the maximum value in the dictionary which must be the count of the items. (I could have used the current value of orderCount instead.)
Questions?
How do I write this linq query:
List<List<string>> listOfLists = new List<List<string>>();
listOfLists.Add(new List<string>(){"Item1", "Item2"});
listOfLists.Add(new List<string>() { "Item2", "Item2" });
//Does listOfLists contain at least one list that has one or more items?
It sounds like you're trying to find if any list has any items. Two ways of doing that:
As described, using Enumerable.Any at both levels (once with a predicate and once without):
var any = listOfLists.Any(list => list.Any());
Just flatten it and see if there are any items at all, as if there is at least one item, it must belong to a list with at least one item:
var any = listOfLists.SelectMany(list => list).Any();
So I have this list, it returns an ID and a thumbnail. ex. List<PersonPicture>
and I have this list, List<Person> which has a property named "picture" in it.
Is there anyway that I can merge this two properties and add the List<PersonPicture> to the property named "picture" in it and base this via the ID since they have the same?
Any help would be appreciated.
You can use an anonymous object for this, below an example:
List<PersonPicture> pictures = LoadPictures();
List<Person> persons = LoadPersons();
var result = persons.Select(pers => new
{
Id = pers.Id,
Name = pers.Name,
Picture = pictures.Where(pic => pic.PersId == pers.Id)
.FirstOrDefault()
.Thumbnail
};
Another solution is to use a Join:
var result = persons.Join(pictures,
pers => pers.Id,
pic => pic.PersId,
(pers, pic) => {
return new
{
Id = pers.Id,
Name = pers.Name,
Picture = pic.Thumbnail
};
});
LINQ isn't quite designed for modifying existing collections like this, but you can do it:
foreach (tup in people
.Join(
picture,
person => person.ID,
picture => picture.ID,
Tuple.Create
))
{
tup.Item1.Picture = tup.Item2;
}
EDIT: Note that this will produce unpredictable results if a person has more than one picture. Is this a possibility, and how should it be dealt with?
You could either use a Join or the Zip operator in linq. These links will take you to questions about the syntax of using both of them. Basically the Join just adds the two lists together based on a key just like in SQL and the Zip merges the two lists by matching the position of each element in each list..
You want to join the two lists based on a shared key -- the ID.
Basically, you want to use the Join operator in LINQ to find pairs of Person and PersonPicture that match the same ID:
persons.Join(pictures, // join these two lists
person => person.Id, // extract key from person
personPicture => personPicture.PersonId, // extract key from picture
(person, personPicture) => ??? // do something with each matching pair
The question you now face is what to do with each matching pair; Join lets you supply a delegate that takes a matching pair and returns something else, and the result of the Join operation will be a list of those 'something else's produced from each of the matching pairs.
Your problem is that you want to take each pair and do something with it -- specifically, you want to copy the picture from the PersonPicture object to the Person object. Since LINQ is all about finding data but not modifying it, this is not trivial.
You can do this in two ways. One is to create a temporary object from each pair, and then iterate over that and do your thing:
var pairs = persons.Join(pictures,
person => person.Id,
personPicture => personPicture.PersonId,
(person, personPicture) => new { person, personPicture };
foreach (var pair in pairs)
pair.person.Picture = pair.personPicture.Thumbnail;
(You can use a Tuple instead of a temporary object, as was suggested in another answer).
This works, but seems clumsy because of the temporary object (be it an anonymous object or a tuple).
Alternatively, you can do the assignment right inside the delegate, and return the Person object itself, since you're done with the PersonPicture object:
var personsWithPicturesPopulated = persons.Join(pictures,
person => person.Id,
personPicture => personPicture.PersonId,
(person, personPicture) => {
person.Picture = personPicture.Thumbnail;
return person;
});
This has the added bonus of giving you the list of persons for which you found a match in the personPictures list, omitting the ones without a match; this is sometimes exactly what you need (and other times it isn't, in which case you can discard the result of the join).
i have a list of filter names: FILTERBYNAMES
my query result items each contain a name list: NAMES
I want to filter the result an take all items whose name list contains at least one name in the FILTERNAMELIST:
results= result.where(r=>r.NAMES.CONTAINS(...?)...?
I think you need something like:
var results = list.Where(i => i.Names
.Any(name => filterNameList.Contains(name)));
You can solve this by looking at the intersection of the two name sets.
var filteredResult = result.Where(i => i.Names.Intersect(filter).Any());
To limit the enumerations of the filter, you could use a hashset...
HashSet<string> hashedFilter = new HashSet<string>(filterByNames);
var results = result
.Where(x => x.Names
.Any(name => hashedFilter.Contains(name))
);